The present invention relates to the manufacture of objects. More particularly, the invention provides a technique including a device for planarizing a film of material of an article such as a semiconductor wafer. However, it will be recognized that the invention has a wider range of applicability; it can also be applied to flat panel displays, hard disks, raw wafers, MEMS wafers, and other objects that require a high degree of planarity.
The fabrication of integrated circuit devices often begins by producing semiconductor wafers cut from an ingot of single crystal silicon which is formed by pulling a seed from a silicon melt rotating in a crucible. The ingot is then sliced into individual wafers using a diamond cutting blade. Following the cutting operation, at least one surface (process surface) of the wafer is polished to a relatively flat, scratch-free surface. The polished surface area of the wafer is first subdivided into a plurality of die locations at which integrated circuits (IC) are subsequently formed. A series of wafer masking and processing steps are used to fabricate each IC. Thereafter, the individual dice are cut or scribed from the wafer and individually packaged and tested to complete the device manufacture process.
During IC manufacturing, the various masking and processing steps typically result in the formation of topographical irregularities on the wafer surface. For example, topographical surface irregularities are created after metallization, which includes a sequence of blanketing the wafer surface with a conductive metal layer and then etching away unwanted portions of the blanket metal layer to form a metallization interconnect pattern on each IC. This problem is exacerbated by the use of multilevel interconnects.
A common surface irregularity in a semiconductor wafer is known as a step. A step is the resulting height differential between the metal interconnect and the wafer surface where the metal has been removed. A typical VLSI chip on which a first metallization layer has been defined may contain several million steps, and the whole wafer may contain several hundred ICs.
Consequently, maintaining wafer surface planarity during fabrication is important. Photolithographic processes are typically pushed close to the limit of resolution in order to create maximum circuit density. Typical device geometries call for line widths on the order of 0.5 xcexcM. Since these geometries are photolithographically produced, it is important that the wafer surface be highly planar in order to accurately focus the illumination radiation at a single plane of focus to achieve precise imaging over the entire surface of the wafer. A wafer surface that is not sufficiently planar, will result in structures that are poorly defined, with the circuits either being nonfunctional or, at best, exhibiting less than optimum performance. To alleviate these problems, the wafer is xe2x80x9cplanarizedxe2x80x9d at various points in the process to minimize non-planar topography and its adverse effects. As additional levels are added to multilevel-interconnection schemes and circuit features are scaled to submicron dimensions, the required degree of planarization increases. As circuit dimensions are reduced, interconnect levels must be globally planarized to produce a reliable, high density device. Planarization can be implemented in either the conductor or the dielectric layers.
In order to achieve the degree of planarity required to produce high density integrated circuits, chemical-mechanical planarization processes (xe2x80x9cCMPxe2x80x9d) are being employed with increasing frequency. A conventional rotational CMP apparatus includes a wafer carrier for holding a semiconductor wafer. A soft, resilient pad is typically placed between the wafer carrier and the wafer, and the wafer is generally held against the resilient pad by a partial vacuum. The wafer carrier is designed to be continuously rotated by a drive motor. In addition, the wafer carrier typically is also designed for transverse movement. The rotational and transverse movement is intended to reduce variability in material removal rates over the surface of the wafer. The apparatus further includes a rotating platen on which is mounted a polishing pad. The platen is relatively large in comparison to the wafer, so that during the CMP process, the wafer may be moved across the surface of the polishing pad by the wafer carrier. A polishing slurry containing chemically-reactive solution, in which are suspended abrasive particles, is deposited through a supply tube onto the surface of the polishing pad.
CMP is advantageous because it can be performed efficiently, in contrast to past planarization techniques which are complex, involving multiple steps. Moreover, CMP has been demonstrated to maintain high material removal rates of high surface features and low removal rates of low surface features, thus allowing for uniform planarization. CMP can also be used to remove different layers of material and various surface defects. CMP thus can improve the quality and reliability of the ICs formed on the wafer.
Many other limitations, however, exist with CMP. Specifically, CMP often involves a large polishing pad, which uses a large quantity of slurry material. The large polishing pad is often difficult to control and requires expensive and difficult to control slurries. Additionally, the large polishing pad is often difficult to remove and replace. The large pad is also expensive and consumes a large foot print in the fabrication facility. These and other limitations still exist with CMP and the like.
What is needed is an improvement of the CMP technique to improve the degree of global planarity that can be achieved using CMP.
According to specific embodiments of the present invention, a technique including an apparatus for chemical mechanical planarization of objects is provided. In an exemplary embodiment, the invention provides an apparatus, which allows the polishing pad to be easily replaced. The apparatus includes a smaller polishing pad, relative to the size of the object being polished.
In a specific embodiment, the present invention provides an apparatus for chemical mechanical planarization. The apparatus has a platen assembly for holding an object (e.g., wafer, disk, flat panel, glass) to be planarized. The apparatus also has a polishing head coupled to a polishing pad, which has a smaller diameter than the object. The polishing head is movable (e.g., pivotable, rotatable, translational) from a first region overlying the platen assembly to a second region, which is outside the first region. A removable puck is coupled between the polishing pad and the polishing head. The removable puck is removably coupled to a coupling on the polishing head. The apparatus also has a first magazine disposed in the second region. The first magazine houses at least one puck comprising a first polishing pad to be placed on the coupling on the polishing head. In a specific embodiment, the magazine houses a polishing pad or a plurality of them to be used to replace a used, worn, or faulty polishing pad in an improved manner.
In accordance with an aspect of the present invention, a system for chemical mechanical planarization comprises a platen assembly for holding an object to be planarized and a polishing head comprising a puck holder assembly for coupling to a substrate for holding a polishing pad. The polishing pad is smaller in surface area than the object. The polishing head is movable from a first region overlying the platen assembly to a second region. The puck holder assembly comprises a backing surface for positioning the substrate, and a clamp ring positioned proximate to the backing surface for supplying mechanical force to the substrate to hold the substrate in place during a polishing operation.
In accordance with another aspect of the invention, a chemical mechanical planarization apparatus comprises a housing including a backing surface for positioning a substrate holding a polishing pad which is smaller in surface area than an object to be planarized by the polishing pad in a polishing operation. A clamp ring is positioned in the housing proximate to the backing surface and being movable between a contracted position to clamp the perimeter of the substrate and an expanded position to release the substrate. A spring mechanism is disposed in the housing for resiliently biasing the clamp ring toward the contracted position.
In accordance with another aspect of the invention, a method for chemical mechanical planarization of an object comprises coupling a polishing head to a substrate for holding a polishing pad which is smaller in area than the object. A resilient mechanical force is applied to the perimeter of the substrate with the polishing head to hold the substrate in place during a polishing operation. The polishing pad is placed in contact with the object and rotated with the polishing head.
Numerous benefits are achieved by way of the present invention over other techniques. In some embodiments, the present invention provides an improved way to attach and remove the polishing pad. Additionally, the invention provides an improved technique for the manufacture of objects. In other embodiments, specific embodiments of the invention provide an easy way to replace used or worn or faulty polishing pads. Depending upon the embodiment, one or more of these benefits may exist. These and others will be described in more detail throughout the present specification and more particularly below.
Embodiments of the present invention achieve these benefits in the context of known process technology and known techniques in the mechanical arts. However, a further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and attached drawings.